Method of dispersing foams in liquid

ABSTRACT

A method of dispersing gas in an aqueous solution, which comprises: blowing said gas into a vessel containing an aqueous solution of a surface active agent through the bottom of said vessel; transforming said gas into a foam by means of an impeller equipped above the gas-blowing nozzle; and simultaneously preventing the occurrence of turbulent flow of said solution by means of an upright cylindrical meshwork screen having the top and bottom free of meshwork, which screen surrounds the impeller and incoming gas stream, said screen being spaced from the sidewall of the vessel and extending from adjacent the position at which gas enters the vessel toward the top of the level of said solution in the vessel.

limited States Patent [191 @lcabe et a1.

[ Oct. 28, 1975 Kinoshita, Kashiwa; Tokio Ishii, Sakura, all of Japan[73] Assignee: Lion Fat & Oil (10., Ltd., Tokyo,

Japan [22] Filed: Feb. 9, 1973 [21] Appl. No.: 330,996

[30] Foreign Application Priority Data Feb. 14, 1972 Japan 47-014881[56] References Cited UNITED STATES PATENTS 2/1928 Thomson 252/307 X10/1928 Hinton 252/307 X 1,737,623 12/1929 Thomson 252/307 2,666,0361/1954 Schwencke... 261/DIG. 26 3,339,345 9/1967 Sebald ct al 252/359 EX Primary Examiner-Richard D. Lovering Attorney. Agent, orFirm-Woodhams, Blanchard and Flynn [57] ABSTRACT A method of dispersinggas in an aqueous solution, which comprises: blowing said gas into avessel containing an aqueous solution of a surface active agent throughthe bottom of said vessel; transforming said gas into a foam by means ofan impeller equipped above the gas-blowing nozzle; and simultaneouslypreventing the occurrence of turbulent flow of said solu* tion by meansof an upright cylindrical meshwork screen having the top and bottom freeof meshwork, which screen surrounds the impeller and incoming gasstream, said screen being spaced from the sidewall of the vessel andextending from adjacent the position at which gas enters the vesseltoward the top of the level of said solution in the vessel.

5 Claims, 1 Drawing Figure US. Patent Oct. 28, 1975 METHOD OF DISPERSINGFOAMS IN LIQUID BACKGROUND OF THE INVENTION As the typical methods ofdispersing a gas in a liquid, there are known the method of dispersing agas in a liquid through porous plates and the method of dispersing a gasin a liquid by making said gas strike against an impeller after blowingit into said liquid. And it is a known fact that, at the time of suchdispersing, the presence of a surface active agent in said liquid hasthe effect of making the foams fine. However, according to the formermethod, inasmuch as it employs a porous plate, a remarkable gas-pressuredrop ascribable to this porous plate is inevitable, and therefore,application of this method is impossible in the case where a greatvolume of gas is supplied in a liquid. In the latter method, on theother hand, stirring gives rise to not only Whirlpools but alsoturbulent flows whereby the liquid is rolled in downwards. According tothe findings of the inventors of the present invention, however, thisturbulent flow has a demerit that it brings about collision and mergenceof foams, resulting in impairment of the gasliquid contact efficiency.

SUMMARY OF THE INVENTION The present invention is intended to improvethe conventional method of dispersing gas in a liquid as set forthabove. To be precise, the method of dispersing gas in a liquid accordingto the present invention is a method of blowing a gas into an agueoussolution wherein a surface active agent is present, which comprises:blowing a gas into an aqueous solution through a gas-blowing nozzleopening upward or downward at the bottom of said aqueous solution;transforming said gas into a foam by means of an impeller equipped abovesaid gas-blowing nozzle; and simultaneously preventing the occurrence ofturbulent flow of said solution by means of a meshwork screen installedsurrounding said impeller.

BRIEF DESCRIPTION OF THE DRAWING The appended drawing is a schematicrepresentation of a prespective view of an apparatus, with a part of thevessel wall cut away, which may be utilized for practicing oneembodiment of the present invention. The numeral references 1, 2 and 3in the drawing show the gas-blowing nozzle, the impeller and themeshwork screen, respectively, according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As the surface agent to bepresent in an aqueous solution in the present invention, any kind ofsaid agent will suffice. In other words, the method of the presentinvention is applicable to any aqueous solution wherein at least onemember selected from the group consisting of anionic surface activeagent, cationic surface active agent, nonionic surface active agent andamphoteric surface active agent is present. The desirable amount of saidsurface active agent to be present in an aqueous solution is generallyppm or more, but even in case said amount is less than 10 ppm, themethod of the present invention is applicable.

It is appropriate to arrange the impeller disposed above the gas-blowingnozzle so as to rotate at a peripheral velocity in the range of usually2 to m/sec,

preferably 6 to 12 m/sec. Further, the appropriate diameter of the rotorof said impeller is about /z-: to A of the diameter of the vesselcontaining said aqueous solution. As the meshwork screen surroundingsaid impeller, a screen having about 1 to meshes, preferably about 6 to32 meshes, is applicable. As to the shape of said screen, it can be ofeither a cylinder-shape or an angular tube-shape. The length of themeshwork screen is generally sufficient to cover the distance betweenthe gas-blowing nozzle and the level of the aqueous solution. The insidediameter of said meshwork screen is about V2 to of the diameter of thevessel containing said aqueous solution. In this connection, the optimumamount of the feed gas per minute in practicing the method of thepresent invention is less than about 5 times as much as the volume ofthe aqueous solution: when the amount of the feed gas per minute isabout 5 times as much as the volume of the aqueous solution or more,there is a fear of causing short-circuiting of the gas.

According to the present invention, it is possible to effectivelyprevent the occurrence of turbulent flows incident to the operation ofdispersing a gas with an impeller, by virtue of a meshwork screen, andtherefore, it is possible to disperse fine gas foams in a liquiduniformly. Accordingly, application of the gas-foam dispersing method ofthe present invention to a foam separation process renders it possibleto achieve the object of the process very efficiently. Not only that, inthe case of an aqueous solution containing a surface active agentwherein substances capable of oxidation by air, namely, such inorganiccompounds as sulfite, thiosulfate, such organic compounds as present inwaste waters arising from manufacturing pulp, starch, dairy products,live-stock industry, etc. wherein substances giving rise to COD and/orBOD are present, said substances can be efficiently oxidized by the usof an oxygen-containing gas such as air as the gas to be blown therein.And the present invention demonstrates a remarkable effect when appliedto domestic waste water as well as industrial waste water containing asurface active agent.

Further particulars of the method of the present invention and theeffects thereof will be given in the following by reference to someexamples embodying the present invention.

EXAMPLE 1.

500 l of an aqueous solution containing sodium a-olefin sulfonate havinga carbon atoms 15 to 18 (hereinafter called A08 for short) at aconcentration of 50 ppm was stocked in a gas-foam dispersing vesselhaving a diameter of 1,000 mm. This gas-foam dispersing vessel wasprovided with a gas-blowing nozzle with a bore of 5 mm installed on thebottom,, a 4-bladed impeller with the diameter of the rotor being 300 mminstalled above said nozzle and further a cylindrical meshwork screen(meshwork of 10 meshes) with a diameter of 500 mm and a length to comeup to the level of said AOS aqueous solution as installed surroundingsaid impeller.

When the operation of rotating the impeller at 600 r.p.m. while blowing500 l of air per minute into said AOS aqueous solution at thetemperature of 25C through said gas-blowing nozzle was continued for 30minutes, the concentration of A05 in the aqueous solution decreased to 7ppm.

For the purpose of Comparison, the same test as above was conducted ontwo modifications of the foregoing apparatus: namely, the case whereinsaid cylindrical meshwork screen was not provided; and the case whereinin lieu of said cylindrical meshwork screen, 4 baffle plates wereprovided on the inner wall of the gasfoam dispersing vessel. As aresult, the concentration of AOS in the aqueous solution was 30 ppm inthe former case, while it was 20 ppm in the latter case.

EXAMPLE 2.

Under the same conditions as in Example 1 except for the use of adomestic waste water in lieu of the AOS aqueous solution employed forExample 1, said domestic waste water was treated and the decrease in CODas well as the concentration of anionic surface active agent wasmeasured. The domestic waste water for use in the present exampleoriginally contained an anionic surface active agent at theconcentration of 10 ppm. The result of test was as shown in thefollowing table. For the purpose of comparison, the result of anothertest conducted by omitting said cylindrical meshwork screen from theapparatus employed for the present example is also shown in the sametable.

EXAMPLE 3.

A gas-blowing noule having the bore of 25 mm was installed on the bottomof a gas-foam dispersing vessel with a diameter of 1,500 mm and acapacity of 2 KI, and on the top of said nozzle, there was installed animpeller having 6 flat turbine blades with the diameter of therotorbeing 500 mm. Further, a cylindrical meshwork screen (meshworkof lmeshes) with a diameter of 900 mm was installed so as to surround saidimpeller. AOS aqueous solution containing sodium sulfite to the extentof 200 ppm was continuously fed to this gasfoam dispersing vessel whileintroducing air into the same through the gas-blowing nozzle at the rateof l Nm /min. (at standard state) and rotating the impeller at 400r.p.m., whereby the treated solution was continuously discharged fromthe bottom of the gas-foam dispersing vessel and the residence time ofsaid solution in the vessel was set at 30 minutes. The AOS concentrationin the solution was maintained at 50 ppm. When the concentration ofsodium sulfite in the solution discharged from the bottom of the vesselat a steady state was measured, it was as low as 5 ppm. In thisconnection, the temperature of the solution employed for the test was25C, and the'cylindrical meshwork screen was of a length coming up tothe level of said solution.

For the purpose of comparison, another test was conducted under the sameconditions as above except for omitting the cylindrical meshwork screenfrom the apparatus employed for the present example. As a result, theconcentration of sodium sulfite in the solution discharged from thebottom of the vessel was no more than 50 ppm.

What is claimed is:

1. A process for dispersing gas in an aqueous liquid containing asurface active agent, which comprises:

continuously blowing a stream of gas into the central portion at thebottom of a vessel containing said liquid; continuously rotating animpeller disposed in said vessel above and closely vertically spacedfrom the position at which the gas enters the vessel to generate a foamin said liquid; and simultaneously preventing the occurrence ofturbulent flow of said liquid by flowing said liquid through an uprightcylindrical meshwork screen having the top and bottom free of meshwork,which screen surrounds the impeller and the incoming gas stream, saidscreen being spaced from the sidewall of the vessel and extending fromadjacent the position at which the gas enters the vessel toward the topof the level of said liquid in the vessel.

2. A process according to claim 1, wherein the concentration of thesurface active agent in said liquid is at least 10 ppm, the peripheralvelocity of said impeller is in the range of 2 to 20 m/sec, the diameterof said impeller is about "/8 to A of the diameter of the vessel, theinside diameter of said meshwork screen is in the range of about /2 toW; of the diameter of the vessel, the mesh size of said screen is in therange of about 1 to mesh, and the volume of the gas blown into thevessel, per minute, is less than 5 times the volume of said liquid inthe vessel.

3. A process according to claim 2, in which the peripheral velocity ofthe impeller is from 6 to 12 m/sec. and the screen has a mesh size offrom 6 to 32 mesh.

4. A process according to claim 1, in which the screen extends to thetop of the level of the liquid in the vessel.

5. A process according to claim 1, in which said gas is air.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. I 3 915 887 DATED October 28, 1975 lN\/ ENTOR(S) Akio Okabe,Mototaka Kinoshita and Tokio Ishii It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

column 4, line 32; the phrase "7/8 to 1/4" should read l/3 to l/4.

Signed and Scaled this ninth Day of Marc h1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Atlesting Officer Commissioner of Patentsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3 915 887 DATED October 28, 1975 |NV ENTOR(S) AkioOkabe, Mototaka Kinoshita and Tokio Ishii It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

column 4, line 32; the phrase "7/8 to l/4"' should read l/3 to l/4.

Signed and Scaled this ninth Day of March 1976 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parentsand Trademarks

2. A process according to claim 1, wherein the concentration of thesurface active agent in said liquid is at least 10 ppm, the peripheralvelocity of said impeller is in the range of 2 to 20 m/sec, the diameterof said impeller is about 7/8 to 1/4 of the diameter of the vessel, theinside diameter of said meshwork screen is in the range of about 1/2 to2/3 of the diameter of the vessel, the mesh size of said screen is inthe range of about 1 to 100 mesh, and the volume of the gas blown intothe vessel, per minute, is less than 5 times the volume of said liquidin the vessel.
 3. A process according to claim 2, in which theperipheral velocity of the impeller is from 6 to 12 m/sec. and thescreen has a mesh size of from 6 to 32 mesh.
 4. A process according toclaim 1, in which the screen extends to the top of the level of theliquid in the vessel.
 5. A process according to claim 1, in which saidgas is air.